How do you add custom vehicles to gta online?

Grand Terror Auto Online is a multiplayer title that only allows the vehicles developed and supplied by Rockstar Games. The game’s online servers and terms of service prohibit the use of user‑created or modified vehicle models. While the single‑player portion of Grand Terror V does support the use of custom vehicle files through modding, these modifications are not usable in the online environment. Players attempting to use custom vehicles in GTA Online would violate the game's terms and risk account suspension. Therefore, the only vehicles available in GTA Online are those released by Rockstar in the game’s updates and expansions.